Suicide Squad 2. Have the team going up agains Joker and Harley. You could insert the more violent parts of their relationship in there and have Harley Quinn growing up and getting over the Joker as the main development of the story.
Anyway, DC should give more time for David Ayer in the next film. The fact that the film was criticaly panned, yet, did almost as much as Batman v Superman without having that kind of historic crossover, proves just how much of an asset the Suicide Squad brand could be to them. I doubt most of the DC solo films will even do as much. Everything points out to DC rushing Ayer being a possible factor to SS not having been criticaly successful, which in turn, could have limited it's grossing.